writing ink 
7 
readily believe M. Chnptal's account of its good properties j This differ* 
but J must observe, that it dilfers from the ink commonly used luk^of'^p'l'iuv'^ 
when Pliny wrote, in nothing but the addition of sea-salt, (tor 
which, as being less disposed to deliquate, I should think 
either saltpetre or sulphate of potash, might be advantageously 
substituted) and in the employment of glue instead of gum 
arabic (which Pliny recommends) to give the composition suffi- 
cient tenacity and consistency. Indeed, Pliny, as I lately men- 
tioned, directs glue to be employed with lamp-black instead of 
gum, when the atramentum, or black mixture was intended to 
be applied as a pigment internally to the walls, fee. of houses. 
I have, indeed, found, tliat when lamp-black has been incor- 
porated with common ink, by first rubbing the former in a mor- 
tar, with a mucilage of gum arabic, the writing done with it 
could not be rendered invisible by the Application of muriatic 
acid and, doubtless, such an addition of lamp-black would 
hinder the letters from ever hecoming illegible by age, at least 
within any length of time which the paper and parchment 
could be expected to last. But ink made with this addition 
would require to be frequently shaken or stirred, as the lamp- 
black would otherwise be apt to separate and subside. Glue 
could not be advantageously employed with any ink containing 
tannin, for obvious reasons. 
As all inks in which the colouring matter is mixed with an F-s«ei)tial oil, 
„. . . or .soil it of 
aqueous menstruum or vehicle, are liable to • sufter injury by turpentine, 
wetting, I resolved to make trial of the essential oil, or spirit 
° tiiack, ike 
of turpentine, and to incorporate with it, as intimately as pos- a very durable 
sible, a sufficient portion of finely-powdered lamp-hlack j and 
having done so, I obtained an ink which proved to be suffi- 
rdently black, and flowed from the pen re.idily, and with a re- 
markably smooth and homogeneal effect. I have, indeed, now 
before me several pieces of writing, for which this compositioa 
was employed (dated at Kew, in September, l/<}9) and the 
strokes of the pen, though fine, are as distinct and even as 
possible. Strong niiricand muiiatic acids have been applied to 
different parts of the writing, without impairing the colour in 
the slightest degree; nor did boiling water cause tlie letters to 
run 
